1. Embryology: Development of Body Cavity, Serous Membranes and Gut (I)
M1 Gross and Developmental Anatomy
11:00-11:50 AM, January 8, 2009
Dr. Milton M. Sholley
Professor of Anatomy and Neurobiology

2. The web address listed on syllabus page 29 has changed.
ANIMATIONS:
The web address listed on syllabus page 29 has changed.
The new address is:

3. Dorsal View of the Embryonic Disc at ~Day 15
Cells from the epiblast migrate through the primitive groove
to replace cells of the hypoblast,
thus forming the definitive endoderm.
Primitive groove
Buccopharyngeal
membrane
Cloacal membrane
Epiblast (blue)
Definitive endoderm
Larsen Website
gast.avi

4. Dorsal View of the Embryonic Disc
The animation will depict ingress of cells from the epiblast through
the primitive groove to form the intraembryonic mesoderm (~day 16).
Primitive groove
Buccopharyngeal
membrane
Cloacal membrane
The dashed line shows the
approximate plane of section
used for the cross sectional
drawings on syllabus page 32.
Epiblast (blue)
Definitive endoderm
Larsen Website
gast.avi

5. Differentiation of Intra-embryonic Mesoderm and
Formation of Intra-embryonic Coelom
Cross sections through the embryonic disc
(Syllabus page 30)
~19 days
~20 days
Adapted from: Langman's Medical Embryology

6. is located between and attached to both the Yolk Sac and
The Embryonic Disc
is located between and attached to both the Yolk Sac and
the Amniotic Sac, as shown here at the end of the third week.
Cut edge of
amniotic membrane
The dashed line shows the
approximate plane of section
used for the cross sectional
drawings on syllabus page 30.
Yolk sac
Larsen Website
neurul.avi

7. Differentiation of Intra-embryonic Mesoderm and
Formation of Intra-embryonic Coelom
Cross sections through the embryonic disc
(Syllabus page 30)
~19 days
~20 days
Adapted from: Langman's Medical Embryology

9. the flat embryonic disc is converted by folding
During the fourth week,
the flat embryonic disc is converted by folding
in both lateral and head-to-tail directions
into a 3-dimensional vertebrate body form.
Animation begins
at ~21 days
Animation ends
at ~25 days
Yolk sac
Larsen Website
neurul.avi

10. Lateral Folding of the Embryonic Disc
-Converts the flat disc into a tubular embryo
-Closes-off the intra-embryonic coelom
-Pinches-off the tubular gut from the yolk sac
-Expands amniotic cavity to surround embryo
Cross sections of the embryo (Syllabus page 31)
Adapted from: Langman's Medical Embryology

11. Kidney Aorta Dorsal mesentery Parietal peritoneum Visceral peritoneum
 The abdominopelvic cavity is lined with parietal peritoneum.
 The gut is covered with visceral peritoneum.
 Mesenteries are double layers of peritoneum that connect parietal and visceral layers.
 The space between parietal and visceral layers is called the peritoneal cavity.
Kidney
Aorta
Dorsal mesentery
Parietal peritoneum
Visceral peritoneum
Peritoneal cavity
Intraperitoneal gut

12.  Mesenteries suspend the gut and gut-associated organs
within the abdominopelvic cavity.
 Mesenteries DO NOT suspend the gut and gut-associated organs
within the peritoneal cavity.
 The peritoneal cavity normally contains nothing but a small amount of
fluid that moistens the surfaces of the peritoneum.
 The peritoneal cavity can expand to contain a large amount of
fluid under abnormal circumstances.

13. The animation will start at ~21 days
Head to Tail Folding
The animation will start at ~21 days
and end at ~28 days.
Amniotic cavity
Head end
Tail end
Yolk sac
Larsen Website
folding.avi

14. Head to Tail Folding Note that the head folding causes
relocation of the
heart primordium
and the mesoderm
cranial to it. The
mesoderm cranial
to the heart becomes
the septum transversum
and is relocated from
a cranial to a thoracic
position. The septum
transversum (shown
in green) will form
an important part of
the diaphragm.
Adapted from:
Langman's Medical
Embryology

15. Model of a 5-week embryo (left) and a cross section
at the level of the septum transversum (right). (Syllabus page 33)
Note the location of the pericardioperitoneal canals and the formation of the diaphragm.
Adapted from: Langman's Medical Embryology

16. Formation of the Diaphragm
The coelom is divided into thoracic and abdominal cavities by
Formation of the Diaphragm

17. Division of the Thoracic Cavity
(Syllabus page 34)
Adapted from: Langman's Medical Embryology

18. Diaphragmatic Hernia
It is usually congenital (Bochdalek’s Hernia) and, if it is extensive, it is often associated with severe hypoplasia of the lungs that becomes fatal at birth.
It is more common on the left side of the body because the pericardioperitoneal canal on the left tends to close later than that on the right.
From: Langman's Medical Embryology

19. Head to Tail Folding and Formation of
the Primitive Gut
(Syllabus page 35)
Adapted from:
Langman's Medical
Embryology

20. The animation will start at ~21 days
Head to Tail Folding
The animation will start at ~21 days
and end at ~28 days.
Amniotic cavity
Head end
Tail end
Yolk sac
Larsen Website
folding.avi

21. Formation of the Primitive Gut
resulting from
Head to Tail Folding
Endodermal sheet
Starting at
~20 days
Yolk sac
Ending at
~26 days
Larsen Website
9-1.avi

22. Kidney Aorta Dorsal mesentery Parietal peritoneum Visceral peritoneum
 The abdominopelvic cavity is lined with parietal peritoneum.
 The gut is covered with visceral peritoneum.
 Mesenteries are double layers of peritoneum that connect parietal and visceral layers.
 The space between parietal and visceral layers is called the peritoneal cavity.
Kidney
Aorta
Dorsal mesentery
Parietal peritoneum
Visceral peritoneum
Peritoneal cavity
Intraperitoneal gut

23.  Mesenteries suspend the gut and gut-associated organs
within the abdominopelvic cavity.
 Mesenteries DO NOT suspend the gut and gut-associated organs
within the peritoneal cavity.
 The peritoneal cavity normally contains nothing but a small amount of
fluid that moistens the surfaces of the peritoneum.
 The peritoneal cavity can expand to contain a large amount of
fluid under abnormal circumstances.

24. Derivatives of the ventral mesentery are shown in blue
and derivatives of the dorsal mesentery are shown in red.
From: Langman's Medical Embryology

25. What are the adult derivatives of the primitive gut regions?
See syllabus pages
Foregut becomes what?
Midgut becomes what?
Hindgut becomes what?
Adapted from:
Langman's Medical
Embryology

26. Foregut artery is celiac.
Midgut artery is SMA.
Hindgut artery is IMA.

27. Obliteration of Chorionic Cavity Enlargement of Amniotic Cavityby
Enlargement of Amniotic Cavity
See this series
of diagrams on
page 146 of Larsen
(3rd ed.)
Animation:
Starts at 4 weeks
Ends at 8 weeks
Amniotic cavity
Yolk sac
Chorionic cavity
Larsen Website
amnio.avi

28. Oligohydramnios: Too little amniotic fluid.
Polyhydramnios: Too much amniotic fluid.
For an interesting discussion
of causes and consequences of these two conditions,
see Larsen, 3rd edition, page 490.